Activity Loss of Ethofumesate in Dry Soil by Chemical Degradation and Adsorption

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was applied to dry soils (2%, w/w moisture content) that were either wetted immediately or remained dry for 1 to 8 days prior to wetting. Two degradation products were isolated with thin-layer and column chromatography from soils that were kept dry for 4 days before wetting. The major product was identified as 2,3-dihydro-3,3-dimethyl-2-oxo-5-benzofuranyl methanesulfonate which accounted for more than 80% of the degradation products. The products were detected 1 day after application to dry soil (between 1 and 3% moisture content), while at moisture contents greater than 3% (w/w) very little ethofumesate was degraded. Radiolabeled ethofumesate and breakdown products were extracted with methanol from dry and wetted soils, and the soil samples were oxidized to quantify nonextractable radioactivity. The percentage of nonextracted ethofumesate was at least 5% greater in dry soil than in wet soil. Activity loss of ethofumesate applied to dry soil probably is due to both chemical degradation and strong adsorption.